title: Potassium ion fluxes in corneal epithelial cells exposed to UVB.
abstract: The goal of this study was to investigate the efflux of K(+) from human corneal limbal epithelial cells (HCLE) exposed to ambient levels of UVB, which is known to cause apoptosis, and to examine the effect of K(+) channel blockers on loss of potassium induced by UVB. HCLE cells were exposed to 100-200 mJ/cm(2) UVB, followed by incubation in culture media with 5.5-100 mM K(+), BDS-1, Ba(2+) or ouabain. To measure intracellular cations, cells were washed in 280 mM sucrose and lysed in DI water. K(+) and Na(+) levels in lysates were measured by ion chromatography. HCLE cells showed maximal loss of K(+)(i) 10 min after exposure to UVB and 5.5 mM K(+) media, with recovery of normal K(+) levels after 90 min. Treatment with 1 μM BDS-1 following UVB exposure reduced the loss of K(+) by HCLE cells. Exposure to 0.1-5 mM Ba(2+) inhibited UVB-induced K(+) loss in a time and dose-dependent manner. These results confirm that blocking K(+) channels in HCLE cells exposed to UVB prevents efflux of K(+), confirming that UVB activates K(+) channels in these cells. Electrophysiology data show that K(+) channels remain highly active at least 90 min after UVB exposure. HCLE cells exposed to UVB and incubated in 0.01-1 μM ouabain did not recover from UVB-induced K(+) loss. These data suggest that the Na/K pump may act to restore [K(+)](i) to control levels in HCLE cells following UVB exposure and that the pump is not damaged by exposure to UVB. Incubation of HCLE cells exposed to UVB in medium with 25-100 mM K(+) media prevented K(+) efflux at extracellular concentrations as low as 25 mM (the concentration in tear fluid), maintaining control levels of K(+)(i). In all experiments inward fluxes and intracellular Na(+) levels mirrored K(+) changes, albeit at the expected lower concentrations. The prevention of UVB-induced K(i)(+) loss by 25 mM K(o)(+) is consistent with the possible contribution of the relatively high K(+) concentration in tears to protection of the corneal epithelium from ambient UVB.
authors.affiliation: Department of Biology, Calvin College, 3201 Burton St. SE, Grand Rapids, MI 49546, USA. jubels@calvin.edu
authors.forename: John L
authors.initials: JL
authors.lastname: Ubels
authors.forename: Rachel E
authors.initials: RE
authors.lastname: Van Dyken
authors.forename: Julienne R
authors.initials: JR
authors.lastname: Louters
authors.forename: Mark P
authors.initials: MP
authors.lastname: Schotanus
authors.forename: Loren D
authors.initials: LD
authors.lastname: Haarsma
mesh_terms: D017209:Apoptosis; D002460:Cell Line; D002852:Chromatography, Ion Exchange; D019573:Epithelium, Corneal / Q000378:metabolism / Q000528:radiation effects*; D006801:Humans; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism*; D026902:Potassium Channel Blockers / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism; D012964:Sodium / Q000378:metabolism; D014466:Ultraviolet Rays
chemical_list: D026902:Potassium Channel Blockers; D015221:Potassium Channels; D012964:Sodium; D011188:Potassium